The invention relates to shaped article, especially packaging material, preferably films and particularly preferentially tubes, comprising a cellulose hydrate which has been partially chemically modified by partial chemical reaction with a synthetic reactive polymer comprising a modified polyalkylene oxide, which is capable of reacting with the OH groups in the cellulose hydrate.
The invention also relates to tubular casings having the above chemical structure which are useful as synthetic sausage casings.
The invention also pertains to a process for preparing the above described shaped articles.
Shaped articles of cellulose hydrate, and especially packaging material, can be burnt after use without problems and are also advantageous because they undergo bacterial decomposition relatively rapidly.
A further advantage of shaped articles which are made of a material of the said type is that certain properties of the material change in a desirable manner during its proper use, for example, as a packaging material. This change in properties of cellulose hydrate films, which comprises shrinkage as a result of the loss of water and/or plasticizer, is especially important when the films are used as sausage casings, because it is necessary for the sausage casings to fit the shrinking sausage material so that plump sausages of appetizing appearance are always supplied. Because of their inert properties, sausage casings which are made of synthetic polymers, such as polyamide, polyester, polyvinylidene chloride or the like, do not sufficiently exhibit these advantageous characteristics. Sausage casings of which are made of the said polymers therefore, frequently have an undesirable wrinkled and unappetizing appearance and are therefore unsellable.
The properties and structure of the cellulose hydrate which forms the shaped article can be varied within wide limits by varying the properties and the composition of the viscose, the average degree of polymerization, the spinning and drying conditions during the manufacture of the shaped articles and the plasticizer content thereof.
It has also been proposed to improve the suppleness of plasticizer-free cellulose hydrate by adding fat-like chemical substances which are capable of crosslinking.
However, it has hitherto not yet been possible to completely prevent, or even only adequately restrict, the very large changes in the structure and the properties of the cellulose hydrate, which forms the shaped article, which arise during their proper use, especially on soaking in water and/or drying of the shaped articles, especially tube-shaped articles, for use as a synthetic sausage casing, as a result of a substantial loss of their content of chemical plasticizer.
In the case of synthetic sausage casings based on cellulose hydrate which has been plasticized with a secondary chemical plasticizer, and which have a water vapor-impermeable coating of polymeric material on their inner side, too high of an internal pressure results in the sausage after the loss of the secondary chemical plasticizer in the casing because of the severe shrinkage of the sausage casing which is caused thereby. Due to the embrittlement of the sausage casing which has occured as a result of the loss of plasticizer, there is then a danger that the sausage casing will tear along its entire length when the sausage is cut. If tearing of the casings is prevented by previously moistening or cooling the sausage, a considerable part of the sausage material will be pressed out from the cut surface, in an undesirable manner, as a result of the high internal pressure.
Because of the embrittlement of the sausage casing as a result of the loss of plasticizer, the casings are sensitive to impact when sausages of this type are transported.
The above mentioned undesirable properties of cellulose hydrate sausage casings also cannot be avoided when casings are used which contain a proportion of a fat-like chemical crosslinking agent.